Aircraft equipped with three engines and having the construction summarized above, such as the LOCKHEED L1011 and the McDONNELL DOUGLAS DC-10 or MD-11, are already known. In particular, the third engine is situated, structurally and geometrically, between the horizontal tail section and the vertical tail section and carries the fin of said vertical tail section. These aircraft, the design of which dates back to the 1970s, and some of which are still in service, are equipped with powerful engines to provide long-haul services; however, given the era in which they were designed, these engines generate considerable noise and entail a high fuel consumption. Specifically, the noise generated by the third engine is particularly disturbing to passengers situated in the rear of the cabin, and also to residents living near airports when the aircraft is in the landing or takeoff phase, since the placement of this third engine means that the noise is diffused all around the aft portion of the fuselage.
Hence, this construction has gradually been abandoned to be replaced by a simpler construction of the twin-jet type, resulting in equal performance.
What is currently happening, with the exception of very long-haul aircraft, of the AIRBUS A-340 and BOEING 747 type, is that airliners are mostly being constructed with two engines, such as turbofans, borne symmetrically and respectively by the fuselage wings. Advances in technology which have made it possible to develop particularly powerful high-performance turbofans mean that these twin-jet aircrafts are able not only to make short-haul and medium-haul flights, but the largest of them are also certified to perform long-haul flights in complete safety despite only using two engines, and even despite malfunctioning of one of them.
However, on the other hand, these powerful turbofans have an ever-increasing mass and size, thereby making it necessary for the aircraft structure (fuselage, wings and landing gear in particular) to be designed accordingly so that it can withstand the stresses, and, by virtue of their oversizing, said jet engines also generate a significant noise level both for passengers and residents living near airports (in the takeoff and landing phase), this in spite of the advances made in this field by engine manufacturers.